Low loss conductor



Jan. 16, 1968 G. N. J. MEAD LOW LOSS CONDUCTOR 2 Sheets-Sheet 1 FiledApril 16, 1964 CURRENT FLOW F G. l

DIELECTRIC CONDUCTOR F I 7 INVENTOR GEORGE N.J. MEAD ATTORN EYS' Jan.16, 1968 G. N. J. MEAD 3,364,339

LOW LOSS CONDUCTOR Filed April 16, 1964 2 Sheets-Sheet 2 INVENTOR GEORGEN. J. MEAD F166 WMWWAV ATTORNEYS United States Patent 3,364,389 LOW LOSSCONDUCTOR George N. J. Mead, Robin Lane, Exeter, NH. 63833 Filed Apr.'16, 1964, Ser. No. 369,277 13 Claims. (Cl. 315-168) This invention isgenerally related to low loss electrical conducting devices and moreparticularly is directed to wards a new and improved device forconducting electrical current with very low resistance at normaltemperatures. This invention also contemplates a novel arrangement forcontrolling the flow of electrical current through a low loss electricalconducting device.

As is well known, conventional electrical conductors display inherentresistance to the how of current. For example, in electricallyconductive solids, such as metals and semi-conductors, electrons movingfrom hole to hole through the crystal lattice collide with the atoms ofthe conductor producing vibrations which further impede the movement ofthe current carrying electrons. These collisions and the vibrationsimparted to the atoms of the conductor are forms of electricalresistance and are usually considered as losses since a portion of theavailable electrical energy is converted into heat energy.

In devices such as gas filled tubes, for example, that employ a plasmaas a medium for conducting a flow of electrical current, the IR drop isa function of the ionization potential of the gas. Not only is theionization potential not recovered during deionization but there is aconstant deionization and reionization that takes place within theplasma caused by collisions between the electrons and positively chargedions both in the conducting space and at the walls of the tube. Theselosses increase if the path of the electrical arc is made to curve.

In both of the above devices there is no problem of increasedresistivity from an electron space charge by reason of the fact thatneutralizing positive ions are distributed along the path of theelectrical current. However, in a vacuum tube no such neutralizingeffect is available to overcome the space charge and, as a result, theelectrical conductivity of a vacuum tube is limited by the presence of aspace charge which normally develops in front of the emitting surface ofthe cathode.

Various means have been proposed to reduce the internal resistance inelectrically conductive devices to provide what is termed asuperconductor. In general, the means taken to achieve a superconductivestate is to lower the temperature of the device to an extremely lowpoint, in some instances approaching absolute zero, so that currentcarrying electrons only are made to flow without hindrance fromthermally excited atoms. This technique requires rather elaborate andexpensive equipment to achieve the low temperature conditions in whichthe superconductive phenomenon appears.

It is an object of the present invention, therefore, to provideimprovements in electrical conductors.

Another object of this invention is to provide a new and improved lowloss electrical conductive device.

Still another object of this invention is to provide a low losselectrically conductive device adapted to function at normal or hightemperatures.

A still further object of this invention is to provide an improvedarrangement for controlling the flow of current through an electricalconducting system.

And yet another object of this invention is to provide a novel means foreliminating the effect of a space charge Within a vacuum conductingdevice.

More particularly this invention features a low loss conductorcomprising an evacuated or gas-filled enclosure and having a pair ofspaced electrodes connected to a suitable power source and of opposingpolarity. Disposed between the two electrodes and extendingsubstantially the full distance therebetween is a core having aplurality of parallel passages which extend from end to end thereof. Theends of the core terminate in closely spaced opposition to theelectrodes. The core body is fabricated from electrically conductivematerial while the walls of the passages are coated with a dielectricstratum to prevent short circuiting of the current. In the vacuum modeof the invention, the core is given a positive static charge to providea distributed positive charge along the current path which neutralizesthe negative field of the space charge. The positively charged walls ofthe passages provide a field which extends into the passageways toneutralize the fields of the electrons in the electron cloud, therebyeliminating this source of electrical resistance for improvedconductivity characteristics.

In the case of a gas filled device, the body would be given a negativecharge so as to hold the positively charged ions within the gas and toreduce their transverse mobility to the point where collisions andrecombinations are minimized. In this embodiment, the positively chargedions provide the distributed positive charge to neutralize the electronspace charge.

However these and other features of the invention, along with furtherobjects and advantages thereof, will become more fully apparent from thefollowing detailed description of preferred embodiments of theinvention, with reference being made to the accompanying drawings inwhich:

FIG. 1 is a cross-sectional view in side elevation, somewhat schematic,of a low loss conductive device made according to the invention,

FIG. 2 is a cross-sectional view taken along the line 22 of FIG. 1,

FIG. 3 is a fragmentary view of FIG. 2 on an enlarged scale to showdetails of construction,

FIG. 4 is a somewhat schematic view showing the relationship between thespace charge and the charged passage walls,

FIG. 5 is a view in perspective of a modified core for the low lossconductor,

FIG. 6 is a view in perspective, somewhat schematic, of a modificationof the invention,

FIG. 7 is a cross-sectional view in side elevation, somewhat schematic,of a modification of the FIG. 1 device and showing a device having auni-directional current flow,

FIG. 8 is a view in side elevation, partly broken away, showing a lowloss conductive device suitable for AC operation,

FIG. 9 is a view in side elevation partly broken away and partlyschematic showing the low conductive device employed as a coil, and

FIG. 10 is a schematic arrangement showing the low loss conductor asapplied to a power transmission line system.

Referring now to FIGS. 1 through 3,, the reference character 10indicates a low loss conductor generally organized about a tubularjacket 12 having its inner surface coated with a dielectric stratum 14.Mounted at either end of the jacket 12 and insulated therefrom areelectrodes 16 and 18 being the cathode and anode respectively.

Disposed within the jacket 12 is a conductive core 20 made up of abundle of insulated electrical filaments 22 extending substantially thefull length of the jacket with their ends terminating in close spacedrelation to the electrodes 16 and 18 as best shown in FIG. 1. Eachfilament 22 is sheathed in a dielectric sleeve 24 and preferably bothare circular in cross-section. With this arrangement, the insulatedfilaments 22 when grouped together into a bundle define a series oflongitudinal passages 26 of small cross-section with each filament 22being equally spaced from the center of an adjacent passage 26.

In practice, the device It) is fully sealed and in a preferred form thejacket is evacuated. Each of the filaments is connected to the positiveside of a suitable power source 28 by means of a lead 30 which passesthrough the walls of the jacket and connects to each of the filaments.The lead 30 is insulated and at points of connection with the conductors22, the joints are also insulated for reasons that will presentlyappear.

When the electrodes 16 and 18' are energized a current flows through thepassages 26. Initially, the space charge 32, as shown in FIG. 4, willdevelop adjacent the cathode 16. The space charge will consist of acloud of relatively immobile electrons which inhibit the flow of currentcarrying electrons between the electrodes. This cloud, in effect,increases the internal resistance of the device as in any vacuum tube.However, according to the present invention, this space charge can beeliminated by the filaments 22 providing a positive charge along thewalls of the passages. The charged walls, it will be understood, areinsulated from the flow of electrons to prevent current leakage.

The charged filaments develop positive fields which extend towards thecenter of each passage and have the effect of neutralizing the negativefields of the free electrons in the space charge. In practice, a fewelectrons may accumulate along the walls of the passage as suggested inFIG. 4. However, this sheath of electrons will be relativelyinconsequential since the primary effect of the static positive fieldwill be to neutralize the fields of the electrons.

By provinding a distributed positive charge along the walls of thepassages, the space charge of the electron cloud traveling therethroughwill be neutralized. In practice, it is desirable that the passages bequite narrow to provide a strong field which will be close to theelectrons moving through the passages. By reason of the fact that theeffect of the space charge is substantially eliminated, the device ischaracterized by very low resistance and high current density. This highconductivity permits high current density without overheating and thusmakes the device particularly useful for generating magnetic fields ofhigh intensities.

The resistance of the conductor may be controlled by varying the chargeon the filaments 22. The device may then serve as an electrical valveuseful in circuits of various types.

In practice, the individual filaments which make up the filaments 22 maybe fabricated from various materials. For example, tungsten would besuitable for hightemperature applications and may be coated with asuitable dielectric such as a ceramic material, for example. Coatedstainless steel may be employed to advantage. Also anodized aluminumwires would be useful insofar as the anodized coating would serve toinsulate the filament from the flow of electrons through the passages.Where the device is used to conduct in one direction only, the cathodemay be a thoriated tungsten element and the anode may be of somematerial such as graphite, for example. For two-way conduction, bothelectrodes may be of refractory material, either graphite or tungsten,for example, and for such applications, the coated electrodes would notnormally be desirable. Refractory electrodes may require a cathodeheater for efiicient electron emission. Other types of electron emittersobviously may be employed to advantage.

Various arrangements other than the bundle of insulated filaments may beemployed as a core for use in establishing a positive field along thepath of conduction and thereby neutralize the space charge within thedevice. For example, a one piece metallic core 33, such as shown in FIG.5, may be employed in place of the bundle of filaments. This core isformed with a plurality of insulated internal longitudinal passages 35,each preferably circular in cross-section and coated with a dielectricIi'latertal along the walls thereof to prevent electrical losses. Indevices employing a statically charged core, there would be an automaticcollection of positive charges within the metallic core along thepassage walls to neutralize the negative fields of the free electronsand thereby neutralize the space charge effect. This automaticcollection of positive charges will be produced by reason of thenegatively charged electrons attracting a stratum of positive chargesalong the walls of the core passages; the effect is augmented if thecore is connected to an infinite ground such as the earth. The action isanalogous to the charging of a capacitor, but the effect is similar tothe actively charged superconductor illustrated in FIGS. 1-3.

Another technique for forming a multiplicity of small passages betweenthe electrodes would be to rule fine grooves on metal foil using aprocess similar to that used in the fabrication of diffraction gratings.Such a foil would be ruled along both sides with the grooves on one sidebeing staggered with respect to those on the opposite side. If thegrooves were all parallel to one another, the sheet of foil could berolled into a cylinder with the grooves parallel to the axis of thecylinder so that the current flow would be axial. Alternatively, thegrooves may be ruled as the radii of an annular disk and a plurality ofthese disks may be stacked together, as suggested in FIG. 6, to form anannular core 37 and in this embodiment, the current flow would be radialbetween a center cathode 39 and a surrounding anode 41 rather than axialas in the previous embodiments.

Another technique by which the passages may be formed through the coreis to employ corrugated metal foil and join the layers together. Thismay be done by a sintering process or by utilizing extremely thincontact cement. The passages could be insulated by oxidizing the surfaceof the passages with a suitable oxidizing agent or by electrolyticaction.

In this device, it is desirable to have the positive fields as close aspossible to the electrons flowing through the vacuum along the passages.For this purpose, it is desirable that in the cae of the filament typecore that the filaments be as thin as possible consistent with areasonable strength factor. For example, filaments on the order of .0005to .005 inch in diameter, may be employed. Thin filaments would be moreefficient than thicker ones since the effect of the positive charge onthe electron cloud is partly dependent on how close the filaments may begathered together. Also, the effect of the positive field in the spacecharge is a function of the charge applied to the filament and thethickness of the insulation enclosing the filament. It will beappreciated that if the insulation of the filament is thick, thepositively charged ions would be spaced further from the passage and itseffect on the space charge would be diminished accordingly. The voltagewhich may be applied to the filaments, would have an effect on thecurrent density up to a given level after which any increas in voltagewould add nothing to the operation of the device.

In the gas filled device, the slow moving ions which move in atransverse direction are immobilized to improve current flow. Thepositive ions within the plasma would tend to move along the walls ofthe passages whereas the fast moving electrons would, by reason of thenegaive charge on the core, move unimpeded along the center of thepassages. The effect would be to eliminate the random movement of gasparticles which normally limit the conductivity of the device by reasonof collisions with the current carrying electrons.

Referring now more particularly to FIGS. 5, 6 and 7, there areillustrated flexible superconducting devices embodying features of theinvention and constituting modifications of the invention. In FIG. 7,there is shown a flexible bellows type metal tube 34 covered on itsouter surface by a woven wire protective sheath 36 and having its innersurface covered with a flexible dielectric material 38. Disposed withinthe tube 34 is a core 40 made up of filaments 42 similar to thosedescribed in conjunction with the embodiment of FIGS. 1 through 3. Eachfilament is circular in cross-section so that when gathered into abundle the filaments nest to define a plurality of longitudinal passages44. As before, each of the filaments is covered with a dielectricinsulating layer 46.

Each end of the tube 34 is sealed by means of a cap 48 and 50 with thecap 48 carrying a concave electrode 52 which, in the illustratedembodiment, constitutes the cathode of the superconducting device. Thecap 50 also carries an electrode of concave configuration and thiselectrode serves as the anode in the circuit. Both electrodes are spacedfrom the ends of the core 40 so as not to be in electrical contacttherewith. The anode 54 is formed with a multiplicity of perforations 56which accommodate the filaments 42 which are drawn therethrough forcontact with a concave plate 58. The plate 58 serves as a commonconductor whereby a positive charge may be applied to all of thefilaments which make up the core 40. The plate 58 will be seen to beconnected to the positive side of a suitable power source 60. It will beunderstood that the filaments 42 are insulated from the anode 54 toprevent short circuiting between filaments and the anode.

The system is similar in operation to the FIG. 1 device. That is to say,a positive charge applied to the filaments 42 through the plate 58 willcause positive charges to be formed along the walls of the passageswhich will serve to neutralize the field of the space charge. However,in the FIG. 5 device, the entire assembly is flexible so that it may beemployed in the same fashion as any flexible lead. The device as shownin FIG. 7 is adapted to conduct current in one direction only and assuch may be used as a rectifier. If conduction in two directions isdesired, it is necessary to modify the device in the manner shown inFIG. 8.

In the FIG. 8 embodiment, the construction is generally the same as thatof the FIG. 7 embodiment with the exception that the electrodes areconnected to an AC power source 62. In the rectifier mode of FIG. 7 itis desirable that the ends of the filaments 42 terminate just short ofthe cathode in order to aid in drawing out the electrons from theemitting surface of the cathode. In the two-way mode of FIG. 8, thissame arrangement could be used.

The flexible superconductor such as shown in FIG. 8 has particularutility for use as a coil 64 as illustrated in FIG. 9. A superconductorcoil 64 of this type may be used in a wide variety of applications. Forexample, such a coil may be employed to advantage in an electro-rnagnet,or for any similar applications requiring the development of high-fluxfields without a high heat release. Furthermore, the conductance of thisdevice would not be impaired by either high magnetic flux density or byhigh ambient temperatures.

Referring now more particularly to FIG. there is shown a furthermodification of the invention. In this embodiment a pair ofsuperconductors 66 and 68 of the flexible type described above areemployed in a long-range power transmission line system. The referencecharacter 90 indicates a generating station in FIG. 10 and a substationis indicated by reference character 72 With a load indicated byresistance 73. Connected to each filament core in the superconductors isa battery or generator 74 for applying a positive charge. Thesuperconductive performance of these transmission lines permits the useof lower transmission voltages without reducing the amount of power thatcan be carried by a given line. This is because of lower line losses andhigher current densities. For both A.C. and DC. power transission, lowertransmision voltage oifers may advantages; e.g. it reduces the costofswitch gear etc; furthermore, low voltages can eliminate the coronalosses associated with high voltage lines. For A.C. power transmission,the lower transmission voltages 6 and the resulting close spacingpermitted, reduces the losses from both the inductive and capacitivereactance of the lines.

While the invention has been described with particular reference to theillustrated embodiment, it will be understood that numerousmodifications thereto will appear to those skilled in the art. Also, itwill be understood that the above description and accompanying drawingsshould be taken as illustrative of the invention and not in a limitingsense.

Having thus described the invention, What I claim and desire to obtainby Letters Patent of the United States is:

1. A low loss conductor of electrical current, comprising (a) wallsdefining an enclosure,

(b) a pair of spaced electrodes disposed within said enclosure,

(c) means for energizing said electrodes thereby producing chargedparticles having an associated field within said enclosure,

(d) a core of electrically conductive material disposed between saidelectrodes and said core having at least one passage for electrons toflow between said electrodes, said core being electrically insulatedfrom said electrodes and the inner volume of said enclosure,

(e) means to apply a charge to said core thereby inducing a distributedcharge along the walls of said core passage, said charge being adaptedto neutralize the fields of the particles within said volume and therebyreducing the resistance to current flow along said passage.

2. A low loss conductor of electrical current according the claim 1wherein said core is grounded.

3. A low loss conductor of electrical current according to claim 1wherein said core is formed with a plurality of spaced passages.

4. A low loss conductor according to claim 1 wherein said core comprisesa plurality of electrically conductive filaments electrically insulatedfrom one another and nested together into a bundle extending lengthwisebetween said electrodes.

5. A low loss conductor according to claim 1 wherein said walls and saidcore are flexible.

6. A low loss conductor according to claim 1 including means for varyingthe charge on said core.

7. A low loss conductor according to claim 1 wherein said enclosure isevacuated and said charge is positive.

8. A low loss conductor according to claim 1 wherein said enclosure isgas-filled and said charge is negative.

9. A low loss conductor of electrical current, comprising (a) a flexibletube,

(b) an electrode disposed at each end of said tube,

(c) means for energizing said electrodes, thereby producing chargedparticles having an associated field within said tube,

(d) a bundle of electrically conductive flexible filaments disposedwithin said tube and extending sub stantially the full length thereof,

(e) said filaments being electrically insulated from said electrodes andfrom the interior of said tube,

(f) said filaments nesting with one another to define a plurality ofpassages between said electrodes, and,

(g) means for applying a static charge to said filaments, said chargebeing adapted to neutralize the fields of the particles Within said tubeand thereby reduce the resistance to current flow along said passages.

10. A low loss conductor according to claim 9 including means forVarying said static charge.

11. A low loss conductor according to claim 9 wherein said tube isevacuated and said charge is positive.

12. A low loss conductor according to claim 9 wherein said tube isgas-filled and said charge is negative.

7 8 13. A low loss conductor power transmission system References Citedmchdmg UNITED STATES PATENTS (a) at least a pair of superconductivelines,

(b) each of said lines being of tubular sealed con- 2,584,758 2/1952siiutsman 313193 Struction, 5 2,765,975 10/1956 Lrndenbald 230 69 (c)electrodes disposed at each end of each of said 2,873,399 2/1959 Gamsonlines, 2,899,588 8/1959 Mueller 313-209 (d) means for energizing saidelectrodes thereby pro- 2,926,677 2/1960 Whlte 135:1 ducing chargedparticles having an associated field 2,927,240 3/1960 vfilldershceWithin Said lines, m 2,687,485 8/1954 Tlrlco 313-492 (e) an electricallyconductive insulated core disposed 28692135 1 10/1954 Morton 315-35within each of said lines and extending substantially 2,725,499 11/1955Fleld the full length thereof, 3,128,408 4/1964 G O0drlch et al 31313O(f) said core being formed with at least one passage 3,162,716 12/1964sllvel' lengthwise thereof and McFae (g) means for applying alternatingstatic charges to said cores for neutralizing the fields of charged par-CRIS RADER Pnmary Exammer' ticles within said passages. T. B. JOIKE,Assistant Examiner.

1. LOW LOSS CONDUCTOR OF ELECTRICAL CURRENT, COMPRISING (A) WALLSDEFINING AN ENCLOSURE, (B) A PAIR OF SPACED ELECTRODES DISPOSED WITHINSAID ENCLOSURE, (C) MEANS FOR ENERGIZING SAID ELECTRODES THEREBYPRODUCING CHARGED PARTICLES HAVING AN ASSOCIATED FIELD WITHIN SAIDENCLOSURE, (D) A CORE OF ELECTRICALLY CONDUCTIVE MATERIAL DISPOSEDBETWEEN SAID ELECTRODES AND SAID CORE HAVING AT LEAST ONE PASSAGE FORELECTRONS TO FLOW BETWEEN SAID ELECTRODES, SAID CORE BEING ELECTRICALLYINSULATED FROM SAID ELECTRODES AND THE INNER VOLUME OF SAID ENCLOSURE,(E) MEANS TO APPLY A CHARGE TO SAID CORE THEREBY INDUCING A DISTRIBUTEDCHARGE ALONG THE WALLS OF SAID CORE PASSAGE, SAID CHARGE BEING ADAPTEDTO NEUTRALIZE THE FIELDS OF THE PARTICLES WITHIN SAID VOLUME AND THEREBYREDUCING THE RESISTANCE TO CURRENT FLOW ALONG SAID PASSAGE.